--- In Microscope@yahoogroups.com, "rhamvossen" <r.vossen@...> wrote:

Hi Rolf,

Thanks for your response. I feel I should try out the COL illumination you are
suggesting. I do have a 40x U-Plan Apochromat NA 0.90 dry objective. I have used
it with my darkfield condenser with excellent results. However, to answer your
question about the high magnification: I am fascinated by protists and bacteria.
I know that some very lovely-looking flagellates require this magnification for
their interesting forms to be appreciated. I assume that higher NA with an oil
immersion would give sharper rendition of these subjects. The thing is that I am
using a home-configured bellows system and it's difficult to estimate the
overall magnification when I raise the bellow height and I realised that with
dry lenses, you end up with empty magnification blurr very quickly.
I try your advice, Rolf and thank you again for helping.
>
> Hi,
>
> Using a 100/1.25 with a 1.2-1.4 darkfield condenser will give you COL
(circular oblique lighting) which is in itself a very impressive illumination
technique. If you just want to have darkfield at higher magnification then the
investment in a high NA dry or water immersion objective is worthwile. What
about a normal 60/0.85 objective, that's nearly in the magnification range that
you want. For what do you need the 1000x darkfield?
>
> Rolf
>
>
> --- In Microscope@yahoogroups.com, "grimra" <ralphg@> wrote:
> >
> > Hi all,
> >
> > I am using darkfield illumination for most of my microscope work. It's so
beautiful with the jet-black background and microorganisms looking like Chinese
lamps floating through the night.
> > I have a question though: I want to use higher magnification of say,
700-1000x using an oil immersion objective such as an 100x Olympus Planachromat
with an NA of 1.25 for a BX50 microscope. I am using a cardioid oil darkfield
condenser with an NA of 1.40. Can I use this objective with the condenser as it
is, or do I have to use a stop of some sort for such an objective?
> > Thank so much.
> >
> > Regards,
> >
> > Ralph
> >
>